Considerable debate exists as to the definition of a normal PVR
• Generally, a PVR of <50 mL is regarded as normal in adults
• The absence of residual urine, though clinically useful, does not adequately exclude BOO or lower urinary tract dysfunction, as the intravesical pressure may be sufficient to overcome degrees of outlet obstruction
• Even small PVR volumes may be significant in symptomatic patients, especially those with recurrent infections and bladder calculus
• PVR of >200 mL is abnormal and regular USS surveillance of the bladder and kidneys is recommended due to the risk of upper tract obstruction
• PVR consistently >300 mL is in keeping with chronic retention and intervention may be advisable (unless this represents a low-pressure system in an asymptomatic patient)
• Consistently increased PVR volume is more likely to represent impaired detrusor contractility with or without coexistent BOO, rather than simply being a function of BOO in isolation. It is important to bear this in mind when managing patients with suspected BOO and therefore repeated measurements and correlation with pressure-flow studies are advised
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